The goal of this study is to examine the role of Interleukin 7 (IL-7) in the regulation of osteoclast formation. To test this hypothesis, I will:1. Determine the effects of IL-7 on osteoclast in B220^+ (typical of B-lineage cells) and B220^- cells in bone marrow that are stimulated with M-CSF and RANKL in vitro. a. I will examine the effects of IL-7 on osteoclast formation in unfractionated, B220^+ and B220^- murine bone marrow cell cultures that are treated with M-CSF and RANKL. Bone marrow will be fractionated by FACS. b. I will examine the effect of IL-7 on the expression of RANK mRNA and protein in cultures that are treated with M-CSF and/or RANKL and compare these responses to effects on osteoclast formation. c. I will determine the effects of IL-7 on the ability of RANKL to stimulate NF-kappaB and JNK (c-Jun NH2-terminal kinase) activity in these cultures because these transcription factors are critical regulators of RANK-RANKL signaling pathways.2. Determine the role that IL-7 plays in osteoclast formation by examining IL-7 knockout (KO) mice and the effects that an anti-IL-7 neutralizing antibodies have on cell cultures from WT mice. a. I will examine osteoclast formation in bone marrow cultures of unfractionated, B220^+ and B220^- bone marrow cells from IL-7 KO mice and cultures from WT mice that are treated with neutralizing antibodies to IL-7. b. I will determine the regulation of RANK mRNA and protein levels in cultures of cells from IL-7 KO mice and whether the addition of exogenous IL-7 rescues the phenotype of these mice. c. I will correlate changes in RANK levels with those of NF-1CB and JNK activity in IL-7 KO mice.